While the present invention can be used in any media-handling system or marking system, it will be described for the sake of clarity as used in a typical cut-sheet color electrophotographic marking apparatus.
Generally, in commercial electrophotographic marking apparatus (such as copier/duplicators, printers, or the like), a latent-image charge pattern is formed on a uniformly charged photoconductive or dielectric member. Pigmented marking particles (toner) are attracted to the latent-image charge pattern to develop said image on the dielectric member. A receiver member capable of accepting a charge such as paper is then brought into contact with the dielectric member and an electric field is applied to transfer the marking particles (i.e. the developed image) to the receiver member from the dielectric member. Though there are countless potential substrates or “media” that can serve as receiver members in a marking system (e.g. paper, boxboard, polyester, etc), for clarity and simplicity the receiver member will hereafter in this document be referred to as “media.” After transfer, the media bearing the transferred image is transported away from the dielectric member; the image is then fixed or fused to the media by heat and/or pressure to form a permanent image thereon. In a typical fusing process where the toner is fused to the media, two rolls are used to form a nip through which the media travels during the fusing process. One roll, usually the harder roll, is a fuser roll, the second roll, usually the softer roll, is the pressure roll.
The media sheet is moved from the transfer station, where the image is transferred from the photoconductor (typically a belt or drum) to the media, and passed to the fuser station where the image is fused to the media. If the media experiences unexpected motion during either the transfer or the fusing process, the image on the media may be disrupted. Sheets that are large enough to extend into in both the fuser and the transfer stations at the same time experience motion effects from both processes and thereby risk image disruption; as such, it is preferred to have the media in only one of those stations at a time. There is generally a fixed distance between the transfer station and the fuser station, thus limiting the length of media that can be used in this type of xerographic system.
It is preferred to have sheets completely out of the transfer station before they enter the fuser station to prevent fuser motion from propagating back through the sheet and impacting the transfer process (and vice versa); therefore, media length is often constrained to be smaller than the distance between those two stations. Previous ideas to accommodate larger sheets required a major print engine architecture overhaul and included repositioning the fuser, creating a separate fusing module, extending the length of the print engine frame, etc. All of these methods would increase the overall machine footprint and have substantial manufacturing cost, tooling, and design resource impacts. Therefore, it is very desirable to have a unit that would extend the media-path length between the transfer station and the fuser station and be easily retrofitted into existing machines.